Hydraulic steering

ABSTRACT

The invention concerns a hydraulic steering ( 1 ) with a steering unit ( 2 ) with feedback behavior, a steering motor ( 8 ) connected to the steering unit ( 2 ) via working pipes (L, R), a steering member ( 6 ) and a feedback suppression device ( 9 ), which is located in at least one working pipe (L, R). It is endeavored to change the feedback behavior of such a steering in a simple manner. For this purpose, the feedback suppression device ( 9 ) has a valve arrangement ( 10 ) with hydraulic control inlet (C).

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/714,419 filed on Mar. 6, 2007, which claims foreign priority benefitsunder 35 U.S.C. §119 from German Patent Application No. 10 2006 010697.0 filed on Mar. 8, 2006, the contents of which are incorporated byreference herein.

FIELD OF THE INVENTION

The invention concerns a hydraulic steering with a steering unit withfeedback behaviour, a steering motor connected to the steering unit viaworking pipes, a steering member and a feedback suppression device,which is located in at least one working pipe.

BACKGROUND OF THE INVENTION

Such a steering is known from, for example, DE 10 2004 021 531 A1.

Such a hydraulic steering is preferably used in tractors or otherself-propelled working machines, which are driven in differentenvironments. For example, a tractor must be able to drive on a publicroad to and from a field. Its real work is then performed, when it isdriving in the field. When driving in the street a steering behaviour isdesired that corresponds to that of a normal vehicle. This means thatthe driver must be able to feel a feedback of the steered wheels on thesteering handwheel. For this purpose, it is necessary that the steeringunit has feedback behaviour. Such a steering unit then also has theadvantage that a “self alignment” of the vehicle can take place, thatis, the steered wheels can automatically move to the straight forwardposition, which the driver learns by means of the turning of thesteering handwheel. In many cases, such feedback behaviour is notdesired when driving in the field. Otherwise, the driver would have toconstantly act upon the steering handwheel or another steering memberwith a certain force.

In the steering shown in DE 10 2004 021 531 A1, the feedback suppressiondevice has a valve that is located in a working pipe between thesteering unit and the steering motor. This valve is electricallyactivated and opens, when the steering handwheel is activated.Therefore, a certain effort is required to activate this valve.

SUMMARY OF THE INVENTION

The invention is based on the task of changing the feedback behaviour ofa hydraulic steering in a simple manner.

With a hydraulic steering as mentioned in the introduction, this task issolved in that the feedback suppression device has a valve arrangementwith hydraulic control inlet.

The valve arrangement that forms a substantial part of the feedbacksuppression device is thus purely hydraulically activated. An additionalelectrical system is no longer required to change the feedback behaviourof the steering unit. Hydraulic fluid with the required pressure isavailable in a hydraulic steering anyway, so that only relatively fewadditional measures are required to either activate or deactivate thefeedback suppression device. When the feedback suppression device isdeactivated, the driver feels forces acting upon the steering motor onthe steering member. When the feedback suppression device is activated,the driver does not feel the effects of such forces.

Preferably, the valve arrangement can also be opened by a pressure fromthe steering unit. With this embodiment it is ensured that the steeringunit can also always act upon the steering motor, when the feedbacksuppression device is active. Thus, the steering unit has a higherpriority than the feedback suppression device, so that the feedbacksuppression device does not have to be disconnected or deactivated toenable a steering.

Preferably, the control inlet is connected to an operation mode valvesupplying the control inlet with a higher or a lower control pressure independence of its activation. The operation mode valve can simply be achange-over valve that supplies a higher control pressure to the controlpressure inlet in one position. Depending on the design of the valvearrangement, this for example causes that the feedback suppressiondevice is connected or activated. When, however, the operation modevalve is changed so that the control inlet of the valve arrangement issupplied with a lower control pressure, the feedback suppression deviceis deactivated. Of course, also a reversed switching is possible.

Preferably, the valve arrangement has a pretensioning device, which actsagainst the pressure at the control inlet. Thus, it is ensured that thevalve arrangement and thus the feedback suppression device always assumea defined state. Depending on the effect of the control pressure at thecontrol inlet, this causes that the pretensioning device eitheractivates or deactivates the feedback suppression device.

Preferably, for each working pipe the valve arrangement has a valve thatinterrupts the working pipe in a predetermined state. When the workingpipe is interrupted, a feedback of the steering motor upon the steeringunit is no longer possible. When the valves are open, the desiredfeedback behaviour appears. The use of a valve in each working pipe hasthe advantage that the steering behaviour and also the feedbackbehaviour are “symmetrical”, as the lengths of the hydraulic pipes,which can change their volume when acted upon by a pressure, correspondto each other, when a corresponding valve is located in each workingpipe.

Preferably, a series connection of two two-way valves is located betweenthe two working lines, the connecting point of said two-way valves beingconnected to the control inlet, each two-way valve having an outlet thatis connected to the valve in the working pipe not connected to thetwo-way valve in question. This is a relatively simple method of usingthe higher of the pressures in the working pipes to open the valve inthe other working pipe, as long as the pressure in the working pipe ishigher than the pressure at the control inlet. When this is not thecase, the valves are acted upon via the pressure at the control inlet.

In an alternative embodiment it may be ensured that a pressure reliefvalve is allocated to each valve that can be opened by both the pressureat the control inlet and the pressure in the respective other workingpipe, and in the opened state connects a closing pressure side of thevalve with the related working pipe. As long as the pressure reliefvalve is closed, the closed valve cannot open, as the pressure on theclosing pressure side cannot be removed. This is not possible until thepressure relief valve opens. In this case, the pressure at the controlinlet is on the one hand sufficient to open the valve, so that asteering with feedback behaviour is possible. On the other hand, theopening pressure can also be generated by the hydraulic fluid flowingback from the motor.

Preferably, a power assisted steering valve is connected in parallel tothe steering unit, the steering valve being connected to the workingpipes in an area between the feedback suppression device and thesteering motor. The vehicle can then not only be controlled via thesteering unit, but also via the steering valve. The steering valve can,for example, be a proportional valve. When the steering motor iscontrolled via the steering valve, the feedback suppression device isparticularly advantageous, as it can prevent a movement of the steeringmember, which is caused by the activation of the steering motor by thesteering valve.

Preferably, the operation mode valve is arranged in series with apressure control valve. The pressure control valve ensures that theoperation mode valve always passes on a predetermined pressure to thecontrol inlet. This is a simple manner of ensuring that the controlinlet is neither overloaded by receiving a too high pressure, nor thatit is undersupplied, because the pressure is too low. When the pressurecontrol valve is located between a high-pressure connection and theoperation mode valve, it can also be ensured that also the operationmode valve only has to be dimensioned in accordance with a predeterminedpressure.

Preferably, the steering unit has a load-sensing connection, whosepressure acts upon the valve arrangement against the pressure at thecontrol inlet. Thus, by means of the pressure at the load-sensingconnection the effect of the pressure on the control inlet can beneutralized again. As soon as the driver activates the steering member,for example the steering handwheel, thus activating the steering unit, ahigher pressure occurs at the load-sensing connection, which usuallycorresponds to the highest pressure available at the steering unit. In asimple manner, this pressure is able to override the pressure at thecontrol inlet, either directly or indirectly.

It is particularly preferred that the load-sensing connection isconnected to an auxiliary valve that is located between a pilot controlpipe and a connection with a higher pressure. The connection with thehigher pressure can be the supply connection or the high-pressureconnection of the steering unit. In this case, the activation of thevalve arrangement will cause no large “consumption” of hydraulic fluid.Such consumption could cause a “hard point” in the steering. When thepressure at the load-sensing connection acts upon the auxiliary valve,only a small amount of hydraulic fluid is required to deflect theauxiliary valve or to change its position. This small amount canpractically not be felt by the driver or operator. The auxiliary valvehas the further advantage that the pressure at the load-sensingconnection in the neutral position does not have to be set exactly atthe lowest pressure or tank pressure, when the auxiliary valve has aspring or another resetting device acting against the pressure at theload-sensing connection. The pressure at the load-sensing connectionwould then at least have to overcome the force of the resetting device,before the auxiliary valve is opened.

Preferably, the steering unit has a working pressure connection,relieved in the neutral position of the steering unit to a low-pressureconnection and carrying at a predetermined deflection of the steeringunit the pressure ruling in the controlled working pipe, a pressure atthe working pressure connection acting upon the valve arrangementagainst the pressure at the control inlet. The pressure at the workingpressure connection is also called “S-pressure” or “S-signal”. Asteering unit with such a working pressure connection is available atSauer-Danfoss ApS, Nordborg, Denmark, under the name of OSP-EL. ThisS-signal has the property that, in the neutral position and in a smallband around the neutral position, it is relieved to tank or another areawith a low pressure. When deflecting to the left or to the right, theS-signal always receives the pressure available at the outlet side ofthe set of teeth of the steering unit, that is, practically the pressureavailable in the “left” or “right” working pipe. Thus, a hard point inthe steering is avoided, as no hydraulic fluid is consumed by theload-sensing connection. Further, a clearly defined “non-feedback state”is available, as in the neutral position the S-signal is effectively setat the tank pressure. Further, the concept offers an advantage in theemergency steering situation, where a pressure built up in one of thetwo working pipes will provide an additional certainty for the forcedopening of the valve unit.

In an alternative embodiment it is ensured that the steering unit existsin the form of an “open-center” steering unit and has a pressureconnection, which is connected to a counter-control connection, whosepressure acts upon the valve arrangement against the pressure at thecontrol inlet. In this connection, you take advantage of the behaviourof an “open-center” steering unit. In the neutral position this steeringunit has a connection between the high-pressure connection and thelow-pressure connection, so that in the neutral position of thissteering unit basically the same pressure rules at both the low-pressureconnection and at the high-pressure connection. This pressure is notsufficient to open the valve arrangement. Not until the steering unit isactivated, will the connection between the high-pressure connection andthe low-pressure connection be interrupted, so that the pressurerequired to switch the valve arrangement to the feedback mode builds upvery quickly.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention is described on the basis of preferredembodiments with reference to the drawings, showing:

FIG. 1 is a first embodiment of a hydraulic steering with feedbacksuppression device,

FIG. 2 is a modified embodiment of a feedback suppression device,

FIG. 3 is a third embodiment of the feedback suppression device,

FIG. 4 is a fourth embodiment of the feedback suppression device,

FIG. 5 is a fifth embodiment of the feedback suppression device,

FIG. 6 is a second embodiment of a steering,

FIG. 7 is a third embodiment of a steering,

FIG. 8 is a fourth embodiment of a steering,

FIG. 9 is a modification of the feedback suppression device according toFIG. 8,

FIG. 10 is a second modification of the feedback suppression deviceaccording to FIG. 8,

FIG. 11 is a fifth embodiment of a steering,

FIG. 12 is a sixth embodiment of a steering,

FIG. 13 is a seventh embodiment of a steering,

FIG. 14 is a schematic view explaining the S-signal, and

FIG. 15 is an eighth embodiment of a steering.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic view of a steering 1 with a steering unit 2, herein the form of a “closed-center” steering unit. With a closed-centersteering unit a connection between a high-pressure connection P and alow-pressure connection T is interrupted in the neutral position.

The high-pressure connection P is connected to a pump 4 via a priorityvalve 3, the pump 4 being formed as a variable pump.

Further, the steering unit 2 has the low-pressure connection T, which isconnected to a tank 5.

The steering unit 2 is activated by a steering member in the form of asteering handwheel 6. In a manner known per se it has a set of teeth 7having, for example, an externally toothed gear wheel and an internallytoothed gear ring and serves as measuring motor. By means of adirectional valve, not shown in detail, pressurised hydraulic fluid canbe supplied to one of two working pipes L, R. The working pipes L, R areconnected to a steering motor 8, here in the form of a piston-cylinderunit.

Between the steering unit 2 and the steering motor 8 is located afeedback suppression device 9. The feedback suppression device 9 has avalve arrangement 10, which is, in the embodiment according to FIG. 1,provided with a non-return valve 11, 12 that can be opened in eachworking pipe L, R.

Via a pilot control pipe 13 the working pipe L is connected to thenon-return valve 12 in the other working pipe R. Via a pilot controlpipe 14 the working pipe R is connected to the non-return valve 11 inthe other working pipe L. The pressure in the pilot control pipes 13, 14opens the non-return valves 11, 12 so that a flow can pass them in adirection from the steering motor 8 to the steering unit 2.

Further, the non-return valves 11, 12 are connected to a control inletC, so that a pressure ruling at the control inlet C can open the twonon-return valves 11, 12.

The control inlet C is connected to an operation mode valve 15, whichconnects the control inlet C to either the tank 5 or a referencepressure P_(ref). In the shown position of the operation mode valve 15the control inlet C is relieved to the tank 5. The operation mode valve15 can be activated mechanically, hydraulically, electrically orotherwise.

With such a steering 1, in which the feedback suppression device 9comprises the valve arrangement 10 and the operation mode valve 15, itis possible to set either a non-feedback operation or a feedbackoperation.

In the shown position of the operation mode valve 15, the operation ofthe steering is non-feedback. The two non-return valves 11, 12 areclosed, so that no hydraulic fluid can flow from the steering motor 8via the connections A, B into the valve arrangement 10. Accordingly,there is no feedback on the steering unit 2.

When, however, the steering unit 2 is activated, for example to deflectthe steering motor 8 to the left, the working pipe L is pressurised bythe steering unit 2. The pressure in the working line L opens thenon-return valve 11 in the working pipe L immediately, so that hydraulicfluid can flow to the left working chamber of the steering motor 8. Thefluid displaced from the right working chamber of the steering motor 8is then displaced to the connection B of the valve arrangement 10. Fromhere, it can flow off, as the non-return valve 12 in the working pipe Rhas been opened via the pilot control pipe 13.

As soon as the pressure from the steering unit 2 subsides, the twonon-return valves 11, 12 close and the steering unit 2 is isolated fromthe steering motor 8.

When, however, the operation mode valve 15 is moved in the otherdirection, the control inlet C is acted upon by a reference pressureP_(ref), which opens both non-return valves 11, 12. In this case, thehydraulic fluid displaced from the steering motor 8 is supplied directlyinto the steering unit 2, where it causes a reaction that can usuallyalso be felt at the steering handwheel 6.

The steering unit 2 also has a load-sensing connection LS, which is onthe one side connected to the priority valve 3 and on the other side tothe pump 4. Via a branch line 16 the priority valve 3 is connected to afurther hydraulic consumer, not shown in detail, which also reports itsworking pressure to the pump 4 via a two-way valve 17.

The steering 1 works exclusively with hydraulic signals. The valvearrangement 10 of the feedback suppression device 9 is set by activationof the operation mode valve 15 in such a manner that a feedback of thesteering motor on the steering unit 2 is either possible or notpossible.

FIG. 2 shows a modified embodiment, in which same or similar elementshave the same reference numbers as in FIG. 1.

Two two-way valves 18, 19 are connected in series between the twoworking pipes L, R. A connecting point 20 between the two two-way valves18, 19 is connected to the control inlet C. The two-way valve 18, whichis connected to the working pipe L, has an outlet, which is connectedvia the pilot control pipe 13 to the non-return valve 12 that is locatedin the other working pipe R. In a similar manner, the two-way valve 19,which is connected to the other working line R, has an outlet, which isconnected via the pilot control pipe 14 to the non-return valve 11 inthe first working pipe L.

The mode of functioning is similar to that in FIG. 1. When, for example,the working pipe L is pressurised by the steering unit 2, the non-returnvalve 11 is opened immediately by the pressure in the working pipe. Thenon-return valve 12 in the other working pipe is opened, as the pressurein the working pipe L is led to the non-return valve 12 via the two-wayvalve 18 and the pilot control pipe 13 in such a manner that thenon-return valve 12 opens. In this case, the control inlet C is at a lowpressure, that is, the operation mode valve 15 is in the position shownin FIG. 1.

When, however, the control inlet C is brought to a higher pressure bymeans of the operation mode valve 15, the two two-way valves 18, 19change over and pass the pressure from the pressure outlet C on todirectly open the two non-return valves 11, 12.

FIG. 3 shows an embodiment, in which the non-return valves 11, 12 havebeen integrated in slides 21, 22 of slide valves. The slides 21, 22 arepressed into the shown position by springs 23, 24, as long as thepressure at the control inlet C is lower than a pressure correspondingto the force of the springs 23, 24. In this case, the valve arrangement10 according to FIG. 3 works exactly like the valve arrangement 10according to FIG. 2. In the closed state the non-return valves 11, 12prevent hydraulic fluid from getting to the steering unit 2 from thesteering motor 8. An activation of the steering motor 8 by the steeringunit 2, however, is possible.

When the operation mode valve 15 is switched from the position shown inFIG. 1, the two slides 21, 22 are displaced to the position not shownagainst the force of the springs 23, 24, so that a passage through theworking pipes L, R from the steering motor 8 to the steering unit 2 ispossible. Also the pressures at the connections A, B of the valvearrangement 10 act in the same direction as the pressure from thecontrol inlet C to open the valves in the working pipes L, R.

The valves 11, 12 have a venting to the environment of the springchambers, in which the springs 23, 24 are located. This has theadvantage that these valves 11, 12 do at the same time act as shockvalves, so that the valves located in a following steering unit canstill be used.

The embodiment of the valve arrangement 10 in FIG. 4 corresponds to thatof FIG. 3. Merely the connection between the connections A, B and theslides 21, 22 are missing.

In the embodiment of the valve arrangement according to FIG. 5 the twosprings 23, 24 load the slides 21, 22 so that both working pipes L, Rare open, when the operation mode valve 15 is in the position shown inFIG. 1 and the control inlet C is pressure relieved accordingly.

In the embodiments according to the FIGS. 1 to 4 a non-feedbackoperation is set, when no pressure or only a small pressure is availableat the pressure inlet C.

In the embodiment according to FIG. 5, however, a feedback operation isset, when no pressure or only a small pressure is available at thepressure inlet C.

When a high pressure is available at the pressure inlet C, that is apressure exceeding the force of the springs 23, 24, the slides 21, 22are displaced so that the non-return valves 11, 12 are positioned in theworking pipes L, R. In this case a feedback of the steering motor 8 onthe steering unit 2 is no longer possible.

However, a steering through the steering unit 2 is possible. When, forexample, the working pipe L is exposed to pressure, the non-return valve11 opens and the slide 22 is taken to the position shown in FIG. 5 bythe pressure in the pilot control pipe 13, so that hydraulic fluid canflow off from the steering motor 8.

Whereas in the embodiments according to FIGS. 1 to 5 the valvearrangement 10 is designed so that it has a valve for each working pipeL, R, this is not the case in the embodiment according to FIG. 6. Herethe valve arrangement 10 has only one single valve with a valve slide22, which is pressed to the opening position by the spring 24, when thepressure at the control inlet C is relieved to the tank 5. When,however, the operation mode valve 15 is switched over, the control inletis supplied with the reference pressure P_(ref), so that the slide 22 istaken to the closing position and interrupts the working pipe R.

It is favourable, when this valve is located as close to the steeringunit 2 as possible.

In the embodiment according to FIG. 6, the steering unit 2 is made as anopen-center steering unit, that is, in the neutral position the steeringunit 2 has a connection between the pressure connection P and the tankconnection T. The pressure connection P is connected to the slide 22 viaa counter-control connection 31, so that the pressure in thecounter-control connection 31 acts in the same direction as the force ofthe spring 24.

The force of the spring 24 corresponds to, for example, a pressure of 7bar. Also the springs 23, 24 in the embodiments according to the FIGS. 3to 5 can correspond to a pressure of 7 bar. The reference pressureP_(ref) is, for example, 13 bar, so that the slide 22 is displaced tothe closing position, when the operation mode valve 15 is switched tothe position not shown. In this case a feedback of the steering motor 8on the steering unit 2 is not possible.

When, however, the steering unit 2 is activated, the connection betweenthe pressure connection P and the tank connection T is interrupted, sothat the pressure at the pressure connection P rises very quickly to theoutlet pressure of the pump 4. At least together with the force of thespring 24 this outlet pressure exceeds the pressure P_(ref), so that forthe steering the slide 22 can be taken to the opening position.

In the embodiment according to FIG. 7 a closed-center steering unit 2 isused, in which a connection between the pressure connection P and thetank connection T does not exist in the neutral position either.

The steering unit 2 according to FIG. 7 has a load-sensing connectionLS, which acts upon the slide 22 of the valve arrangement 10 via thepilot control pipe 13 in the same direction as the spring 24.

In the shown switching position of the slide 22 the working pipe R isopen for passage. Due to the position of the operation mode valve 15 thepressure at the tank 5 rules at the control inlet C. In this case afeedback steering behaviour occurs.

When the operation mode valve 15 is switched over, the referencepressure P_(ref) reaches the control inlet C and switches the slide 22,so that the working pipe R is interrupted. In this case a feedback ofthe steering motor 8 on the steering arrangement 2 is not possible.When, however, the steering arrangement 2 is activated, the pressure atthe load-sensing connection LS increases and together with the spring 24it opens the working pipe R in that the slide 22 is displaced to theposition shown.

In FIG. 7 the reference pressure P_(ref) is set by means of a pressurecontrol valve 25, for example at a value of 13 bar. The pressure controlvalve 25 has a valve slide 26, which is loaded in the opening directionby the force of a spring 27 and the pressure at the tank connection T.In the closing direction the valve slide 26 is loaded by the pressure atthe outlet of the pressure control valve 25. The inlet of the pressurecontrol valve 25 is connected to the pressure connection P.

The value of the reference pressure P_(ref) can then be set by selectingthe force of the spring 27.

FIG. 8 shows that the pump 4 is a variable capacity pump, which iscontrolled by the pressure at the load-sensing connection LS. Of course,also here an embodiment is possible with a pump 4 having a fixeddisplacement, that is, an embodiment as in FIG. 7.

In each working pipe the valve arrangement 10 has a non-return valve 11,12. Further, in each working pipe the valve arrangement 10 has a valveslide 21, 22 arranged in parallel, which is pressed into the openingposition against the force of the springs 23, 24 (shown). In this case afeedback steering is possible, as a direct connection between thesteering motor 8 and the steering unit 2 is permanently available.

Only when the operation mode valve 15 is switched so that the referencepressure P_(ref) reaches the control inlet C, the slides 21, 22 aredisplaced against the force of the springs 23, 24, so that the workingpipes L, R are interrupted. In this case there is no feedback of thesteering motor 8 on the steering unit 2.

However, the steering unit 2 can still activate the steering motor 8. Inthe “forward” direction the non-return valve 11, 12 in the relatedworking pipe is opened. In the “return” direction the slide 22 is openedby the pressure at the load-sensing connection LS.

The FIGS. 9 and 10 show modified embodiments of the valve arrangements.

In the embodiment according to FIG. 9 the non-return valves 11, 12 areintegrated in the slides 21, 22.

In the embodiment according to FIG. 10 non-return valves are notavailable. The feedback suppression occurs exclusively through theslides 21, 22, which are opened by the force of the springs 23, 24 toensure feedback behaviour, when the control inlet C is not underpressure. When, however, by means of the operation mode valve 15pressure is acting upon the slides 21, 22, the slides move against theforce of the springs 23, 24 in the closing direction. In this case, anopening of the working pipes L, R is only possible, when the steeringunit 2 generates a correspondingly high pressure at the load-sensingconnection LS, which exceeds the pressure at the control inlet C.

FIG. 11 shows a steering 1, which substantially corresponds to that inFIG. 7. Further, it has a steering valve 28, which is located inparallel to the steering unit 2 between the pressure connection P andthe tank connection T on the one side and the steering motor 8 on theother side. The steering valve 28 ends in the working pipes L, R betweenthe valve arrangement 10 and the steering motor 8, so that the fluidfrom the steering valve 28 is not influenced by the valve arrangement10.

When the pressure at the load-sensing connection LS is used to activatethe valve arrangement 10 directly, a so-called “hard point” may occurduring steering. At the instant, when the valve arrangement 10 isactivated, a small amount of hydraulic fluid will be missing, which canbe felt at the steering handwheel 6.

To remedy this problem, the embodiment according to FIG. 12, whichotherwise corresponds to the embodiment according to FIG. 8 that issupplied with a valve arrangement according to FIG. 10, is provided withan auxiliary valve 29. The auxiliary valve 29 is activated by thepressure at the load sensing connection LS and then creates a connectionbetween the pressure connection P and the pilot control pipe 13, so thatthe slides 21, 22 are acted upon by the pressure of the pressureconnection P against the pressure at the control inlet C. The auxiliaryvalve 29 is switched by an auxiliary valve spring 30, so that the pilotcontrol pipe 13 is connected to the tank 5 again.

This embodiment has two substantial advantages. Firstly, the amount ofhydraulic fluid required to switch over the auxiliary valve 29 issubstantially smaller than the amount of hydraulic fluid required toswitch over the two slides 21, 22. Accordingly, no “hard point” occursduring steering.

Secondly, with this embodiment it is no longer required that the loadsensing connection LS carries the same pressure as the tank 5, when thesteering unit 2 is in the neutral position. As long as the pressure atthe load-sensing connection LS does not exceed the force of the spring30, the auxiliary valve 29 remains in the position, in which the pilotcontrol pipe 13 is isolated from the pressure connection P, so that thepositions of the slides 21, 22 controlled by the operation mode valve 15remain unchanged.

FIG. 13 shows a further amended steering 1, in which the valvearrangement 10 corresponds to that in FIG. 12.

The design of the steering unit has changed. It has a working pressureconnection S, from which an “S-pressure” or an “S-signal” can beobtained, which will be explained by means of FIG. 14.

In the neutral position (FIG. 14 a) the S-signal corresponds to thepressure at the low-pressure connection T. This connection also remainsin a small band around the neutral position. In this case, the pressureat the load-sensing connection LS corresponds to the pressure at thetank connection T.

When the steering unit 2 is activated so that the left working pipe L isexposed to pressure (FIG. 14 b), the S-pressure or the S-signalcorresponds to the pressure in the left working pipe L.

When the right working pipe R is exposed to pressure (FIG. 14 c), theS-signal corresponds to the pressure in the right working pipe R.

Also with this working pressure connection S a hard point in thesteering is avoided, as no pressure from the load-sensing connection LSis required to activate the valve arrangement 10. Further, it gives awell defined non-feedback operation, as in the neutral position theS-signal is effectively set at the pressure at the tank connection T.

Further, a steering arrangement with the working pressure connection Sis advantageous in an emergency steering situation, where the pressurebuilt up at the working pressure connection S provides further safetyfor the opening of the valves in the working pipes L, R, at least in oneof the working pipes L, R.

FIG. 15 shows an eight embodiment of a steering 1, in which a pressurerelief valve 31, 32 is allocated to each valve 11, 12. Each pressurerelief valve is retained in a closed position by a spring 33, 34.

In the direction against the springs 33, 34 acts the pressure at theoutlet of a two-way valve 35, 36. Each two-way valve 35, 36 is on theone side connected to the respectively other working pipe R, L, that isthe working pipe to which the pressure relief valve 31, 32 is notconnected. On the other side the two-way valves 35, 36 are connected tothe control inlet C.

The valve slides 21, 22 of the valves 11, 12 are loaded in the closedposition by the two springs 23, 24.

On the opposite side of the slide 21, 22, that is, in the closingdirection, acts the pressure at the control inlet C or the pressure inthe working pipe L, R allocated to the valve 11, 12, respectively.

Also in the opening direction acts a pressure at the outlet of thevalves 11, 12. This pressure originates from the motor 8, when hydraulicfluid is displaced from the motor 8.

Via a throttle 37, 38 the outlets of the valves 11, 12 are connected tothe side of the valve slides 21, 22, upon which also the springs 23, 24act. At the same time, this side is connected to a pressure relief valve31, 32.

This steering 1 now works as follows:

When a pressure is available at the control inlet C, which exceeds theforce of the springs 23, 24, the pressure at the control inlet C opensthe pressure relief valves 31, 32, so that the slides 21, 22 of thevalves 11, 12 are moved to the opening position. Then the steering 1works with feedback behaviour.

When the pressure at the control inlet C drops so that it is below apressure corresponding to the force of the springs 23, 24, the valves11, 12 are closed, as shown.

When, now, the steering arrangement 2 is activated, for example toexpose the working pipe R to pressure, the valve 12 allocated to thisworking pipe R is opened, as the pressure in the working pipe R actsupon the slide 22 in the opening direction.

At the same time the pressure relief valve 31, which is allocated to theother valve 11, is opened via the two-way valve 35. Accordingly,hydraulic fluid flowing back from the motor 8 can act upon the slide 21in the opening direction. The pressure here is higher than the pressurein the closing direction, as the hydraulic fluid flowing off through thepressure relief valve 31 causes a pressure drop at the throttle 37.Accordingly, the valve 11 is also opened and the motor 8 can beactivated.

In all embodiments the steering unit 2 in itself has feedback behaviour,that is, a pressure change at its outlets, which are connected to theworking pipes L, R, causes that the steering member 6 moves independence of the amount of hydraulic fluid flowing in or out. Thisfeedback behaviour is desired in many cases, but undesired in many othercases. To enable connection or disconnection of this feedback behaviourwithout changing the steering unit 2, the feedback suppression device 9can be operated in a purely hydraulic manner.

While the present invention has been illustrated and described withrespect to a particular embodiment thereof, it should be appreciated bythose of ordinary skill in the art that various modifications to thisinvention may be made without departing from the spirit and scope of thepresent invention.

What is claimed is:
 1. A hydraulic steering comprising: a steering unitwith feedback behaviour; a steering motor connected to the steering unitvia working pipes; a steering member; and a feedback suppression device,wherein the feedback suppression device is located in at least one ofthe working pipes, wherein the feedback suppression device includes avalve arrangement with a hydraulic control inlet, and wherein thefeedback suppression device may be activated or deactivated as afunction of control pressure at the hydraulic control inlet.
 2. Thesteering according to claim 1, wherein the valve arrangement can also beopened by a pressure from the steering unit.
 3. The steering accordingto claim 1, wherein the control inlet is connected to an operation modevalve supplying the control inlet with a higher or a lower controlpressure in dependence of activation of the operation mode valve.
 4. Thesteering according to claim 3, wherein the operation mode valve isarranged in series with a pressure control valve.
 5. The steeringaccording to claim 1, wherein for each working pipe the valvearrangement has a valve that interrupts the working pipe in apredetermined state.
 6. The steering according to claim 5, wherein aseries connection of two two-way valves is located between the twoworking pipes, the connecting point of said two-way valves beingconnected to the control inlet, each two-way valve having an outlet thatis connected to the valve interrupting the working pipe of the othertwo-way valve.
 7. The steering according to claim 1, wherein a powerassisted steering valve is connected in parallel to the steering unit,the steering valve being connected to the working pipes in an areabetween the feedback suppression device and the steering motor.
 8. Thesteering according to claim 1, wherein the valve arrangement has apretensioning device, which acts against a pressure at the controlinlet.
 9. The steering according to claim 1, wherein the steering unithas a load-sensing connection, whose pressure acts upon the valvearrangement against the pressure at the control inlet.
 10. The steeringaccording to claim 9, wherein the load-sensing connection is connectedto an auxiliary valve that is located between a pilot control pipe and aconnection with a higher pressure.
 11. The steering according to claim1, wherein the steering unit has a working pressure connection, relievedin the neutral position of the steering unit to a low-pressureconnection and carrying at a predetermined deflection of the steeringunit the pressure ruling in the deflected working pipe, a pressure atthe working pressure connection acting upon the valve arrangementagainst the pressure at the control inlet.
 12. The steering according toclaim 1, wherein the steering unit exists in the form of an“open-center” steering unit and has a pressure connection, which isconnected to a counter-control connection, whose pressure acts upon thevalve arrangement against the pressure at the control inlet.
 13. Thesteering according to claim 1, wherein the valve arrangement is furtheradapted to be operated by pressure from the steering unit.
 14. Thesteering according to claim 1, wherein the control inlet is connected toan operation mode valve that supplies the control inlet with a controlpressure.